The present invention relates to a technique of generating a predetermined voltage.
There has been proposed a technique (DC-DC converter) that a predetermined voltage is generated under the control of a transistor connected to a DC power source and applied to a driving load. For example, JP-A-2008-236822 proposes a technique of switching a period for controlling the conductive/non-conductive state of a transistor between a low load state and a high load state. To be concrete, two kinds of clock signals, that is, a reference clock signal of a predetermined frequency and a control clock signal of a frequency variable according to a load are generated in parallel, whereby the transistor is controlled in accordance with the reference clock signal in the high load state but controlled in accordance with the control clock signal in the low load state. According to the above configuration, it is possible to reduce an amount of dissipation power in the low load state.
However, according to the technique described in JP-A-2008-236822, since it is necessary to independently provide two kinds of circuits for respectively generating the reference clock signal and the control clock signal, there arises a problem that the circuit configuration is complicated. Further, there arises a problem that the control operation of the transistor becomes discontinuous at the time of switching between the clock signals according to the load.